This invention is directed to a balloon for a blood vessel-dilating catheter.
A balloon catheter having an inflatable balloon secured at its distal end has been applied for various cavities in a living body including a blood vessel. Utility of the balloon catheter is increasing in various medical fields.
Of the balloon catheters mentioned above, a blood vessel-dilating catheter is employed in percutaneous transluminal coronary angioplasty (PTCA) to dilate a stenosis or a narrowing in a blood vessel such as coronary artery. In PTCA, the femoral artery is secured, for example, by the Serdinger method; a guiding catheter is introduced into the thus secured femoral artery and advanced through the lumen of the artery until it reaches near the target lesion, the narrowing in the artery, by manipulating a guide wire; a blood vessel-dilating catheter is introduced into the lumen of the guiding catheter to locate the balloon beyond the distal end of the blood vessel-dilating catheter; and a blood vessel-dilating fluid is introduced into the lumen of the blood vessel-dilating catheter to inflate the balloon to thereby dilate the narrowing in the blood vessel.
Such a blood vessel-dilating catheter is required to have a trackability so that the blood vessel-dilating catheter can smoothly advance through the lumen of the guiding catheter along the tortuous blood vessel to reach the lesion site. The balloon is required to have a sufficient dimensional stability as well as excellent strength and flexibility so as to avoid excessive dilatation of the narrowing of the blood vessel.
Typical balloons for balloon catheters are disclosed in U.S. Pat. Nos. 4,093,484; 4,154,244; 4,254,774; 4,906,244; and 5,108,415; and PCT Application No. JP88/00202.
The balloons described in these patents and patent application comprise a mixture of an ethylene-buthylene-styrene block copolymer and a low molecular weight polystyrene having polypropylene optionally added thereto; a composition similar to the one just mentioned wherein butadiene or isoprene is used instead of the ethylene and the buthylene; polyvinyl chloride; polyurethane; a polyester copolymer; a thermoplastic rubber; a silicone-polycarbonate copolymer; an ethylene-vinyl acetate copolymer; biaxially oriented Nylon 12; biaxially oriented polyethylene terephthalate; polyethylene; a crosslinked ethylene-vinyl acetate copolymer; etc.
The materials particularly used for the balloons of the blood vessel-dilating catheters include polyvinyl chloride (hereinafter abbreviated as PVC), polyethylene (hereinafter abbreviated as PE), biaxially oriented Nylon 12 (hereinafter abbreviated as N12), and biaxially oriented polyethylene terephthalate (hereinafter abbreviated as PET).
Among these, aliphatic high polymers such as PE, PVC, and N12 are highly flexible, realizing a sufficient trackability. These materials, however, are insufficient in their strength to detract from dimensional stability.
PET, on the other hand, has excellent strength and dimensional stability. PET, however, has an excessively high modulus of elasticity due to crystallization caused by the biaxial orientation, and therefore, is inferior in impact strength, tear resistance and flexibility, leading to poor trackability of the catheter.
Furthermore, PET is poor in coating adaptability, adhesibility, and heat sealability to suffer from insufficient operativity and workability in preparing the balloon catheter. In addition, PET inherently lacks antithrombotic properties, and it would be quite difficult to subject the PET to various treatments to impart biocompatibility, in particular, blood compatibility.